Summary:
This change addresses an issue which shows up with the synchronised race
between threads writing into a buffer, and another thread reading the
buffer.
In a lot of cases, we cannot guarantee that threads will always see the
signal to finalise their buffers in time despite the grace periods and
state machine maintained through atomic variables. This change addresses
it by ensuring that the same instance being updated to indicate how much
of the buffer is "used" by the writing thread is the same instance being
read by the thread processing the buffer to be written out to disk or
handled through the iterators.
To do this, we ensure that all the "extents" instances live in their own
the backing store, in a different contiguous page from the
buffer-specific backing store. We also take precautions to ensure that
the atomic variables are cache-line-sized to prevent false-sharing from
unnecessarily causing cache contention on unrelated writes/reads.
It's feasible that we may in the future be able to move the storage of
the extents objects into the single backing store, slightly changing the
way to compute the size(s) of the buffers, but in the meantime we'll
settle for the isolation afforded by having a different backing store
for the extents instances.
Reviewers: mboerger
Subscribers: jfb, llvm-commits
Differential Revision: https://reviews.llvm.org/D54684
llvm-svn: 347280
Summary:
This change cuts across LLVM and compiler-rt to add support for
rendering custom events in the XRayRecord type, to allow for including
user-provided annotations in the output YAML (as raw bytes).
This work enables us to add custom event and typed event records into
the `llvm::xray::Trace` type for user-provided events. This can then be
programmatically handled through the C++ API and can be included in some
of the tooling as well. For now we support printing the raw data we
encounter in the custom events in the converted output.
Future work will allow us to start interpreting these custom and typed
events through a yet-to-be-defined API for extending the trace analysis
library.
Reviewers: mboerger
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D54139
llvm-svn: 346214
Summary:
This change implements a controller for abstracting away the details of
what happens when tracing with FDR mode. This controller type allows us
to test in isolation the various cases where we're encountering function
entry, exit, and other kinds of events we are handling when FDR mode is
enabled.
This change introduces a number of testing facilities we've needed to
better support expressing the conditions we need for the unit tests. We
leave some TODOs for moving those utilities into the LLVM project,
sitting in the `Testing` library, to make matching conditions on XRay
`Trace` instances through googlemock more manageable and declarative.
We don't wire in the controller right away, to allow us to incrementally
update the implementation(s) as we increase testing coverage of the
controller type. There's a need to re-think the way we're managing
buffers in a multi-threaded environment, which is more invasive than
this implementation.
This step in the process allows us to encode our assumptions in the
implementation of the controller, and then evolve the buffer queue
implementation to support generational buffer management to ensure we
can continue to support the cases we're already supporting with the
controller.
Reviewers: mboerger, eizan
Subscribers: mgorny, llvm-commits, jfb
Differential Revision: https://reviews.llvm.org/D52588
llvm-svn: 344488
Dean Michael Berris